1. Technical Field of the Invention
This invention relates to an ignition timing control device for internal combustion engines which controls the ignition timing in response to a knocking state of the engine.
2. Description of the Prior Art
The setting of the ignition timing for an internal combustion engine is carried out for optimum efficiency with regard to the operating state of the engine. In general, it is desirable to set the ignition timing to approach MBT (Minimum advance for Best Torque) as nearly as possible within a range in which knocking, or delayed detonation of unburned pockets of fuel, within the engine does not occur. However, the conventionally employed ignition timing control devices have mostly been mechanical, with ignition advance characteristics that are inconsistent, due to production tolerances and variations due to age. For this reason, it has been necessary to avoid knocking in practice by setting the ignition timing somewhat retarded of the ignition advance characteristics. This has adversely affected the efficiency of the engine. Furthermore, even if an ignition timing control device without production tolerances and variations with age could be provided, the knocking phenomenon itself is influenced by factors such as the temperature and humidity of the engine's intake air, as well as the air-fuel mix ratio, etc., such that setting the ignition timing to avoid knocking under a certain set of conditions cannot eliminate the possibility of knocking under a different set of operating conditions.
In this situation, it is possible to apply a system of detecting the onset of knocking to control the ignition timing in such a way that knocking virtually never occurs, even when errors in the ignition advance characteristics arise due to the aforementioned mechanical tolerances or differences in the operating conditions. Essentially, this means appropriately retarding the ignition timing at the onset of knocking, so as to eliminate knocking.
There are various methods for detecting the onset of knocking, including measuring the pressure inside the combustion chamber, measuring the vibrational acceleration of the engine, and measuring the sound produced by the engine, etc., but in terms of practical application, from considerations such as the siting of the detector and signal processing, etc., the method whereby the vibrational acceleration of the engine is measured is regarded as the most practical. However, with this method, mechanical vibration noises that are unconnected with the knocking produced by the engine are picked up simultaneously with the knocking signal, and so it is necessary to discriminate the knocking signal from among the mechanical vibration noises.